Funds are requested to support the participation of U.S. scientists in a meeting entitled "DNA Repair and Mutagenesis: Mechanism, Control, and Biological Consequences" that will be sponsored by the American Society for Microbiology. This meeting, which will be held at the Westin Hotel, Hilton Head, South Carolina, November 1-7, 1999, will bring together the various sub-disciplines that collectively comprise the field of DNA Repair and Mutagenesis. Conferences of this type have been held at approximately 4-year intervals since 1974 and have played a critical role in the development of this exciting area of research. Attendance is expected to be ca. 500 and careful thought has been given to the choice of site and design of the program so that the participants will be able to enjoy the type of informal interactive environment normally found only at smaller meetings such as Gordon Conferences. The meeting will be international in scope but mechanisms have been devised to encourage the participation of young investigators, postdoctoral fellows, and graduate students. Recent discoveries in the field of DNA Repair and Mutagenesis to be discussed at the meeting have direct relevance to human health, particularly to cancer, aging, human genetic diseases, and the threats posed by environmental mutagens and carcinogens including reactive oxygen species. For example, mutation in the HNPCC (hereditary nonpolyposis colon cancer) genes (encode components of mismatch repair), destabilize the genome and increase cancer incidence. The Blooms (extreme cancer proneness) and the Werner's syndrome (premature aging) genes both have been found to encode proteins of he E. coli RecQ helicase family, opening new doors for exploring the mechanisms underlying cancer susceptibility and aging. The nature of DNA repair/checkpoint defects in Xeroderma pigmentosum, Cockayne, Ataxia telangiectasia, and the Nijmegen breakage syndrome and their relevance to human disease will be discussed. The fundamental science underlying these discoveries will be covered in depth with topics ranging from crystal structure of DNA repair proteins, to the biochemistry of multi protein DNA repair systems, to genetic analyses of cellular responses to DNA damage, to analysis of DNA damage checkpoint control systems.